Best advice I can give is start easy. Install GOS, install Sandboxed Play Services and Play Store according to the official manual and use your phone like before. You'll learn a lot about the features by just browsing and using the phone.
If you build your digital Fort Knox right out of the gate, it will break many apps and convenience features you're used to. Make it smooth and nice.
Other than that, make a threat model so you can assess which features are useful and important to you. GOS gives you full control over your privacy and security, so you can adapt it very close to your needs (if you know them).